1. Field of the Invention
This invention relates to fault-tolerant systems employing electrical connectors. More particularly, it relates to the arrangement of connector pin assignments to enhance fault isolation.
2. Description of the Related Art
One fault-tolerant hardware design strategy for an aircraft navigation/control system is to partition the system into functional areas, sometimes referred to as "fault containment areas", provide redundancy for each area, and provide signal crossfeed and fault detection and isolation at each functional area boundary, for example, at the bus interface. Some examples of these functional areas include accelerometer data systems, a gyroscope data system, processor systems, power supply, power supply monitoring, system clock, and the like.
A fault-tolerant system as just described is configured so that each functional area contains redundant circuit subsystems, each responding to identical inputs, providing identical functions, and therefore providing identical outputs. Thus, if any one or more, but not all, of the redundant subsystems fail, the remaining subsystem or subsystems will continue to function normally so that the overall aircraft navigation/control system may continue to operate, as is well understood in fault-tolerant systems. Herein, such a redundant subsystem is referred to as a "fault containment module".
A fault-tolerant system as described above, like other large electronic systems, commonly employs a plurality of circuit card assemblies, each having a multi-pin connector for insertion into a mating connector on a master interconnect printed wiring board, sometimes referred to as a "mother board."
When multi-pin connectors are used to connect the circuit card assemblies to the mother board, there is a possibility that during insertion of the pins into their sockets, a pin will become bent and will contact an adjacent pin. It is also possible for foreign contaminants to bridge adjacent pins or sockets. In fault-tolerant systems, it is important that a failure of any kind should always be limited to only one fault containment module. That is, if a pin assigned to one fault containment module is bent, then only the fault containment module requiring the electrical signal of that pin should fail, and no others. When this requirement is met, the fault containment modules are said to be isolated from each other.
Previously, in order to provide such isolation, the practice was to use one electrical connector for each interface between fault containment modules. One fault containment module could therefore have its output signals going to several different connectors, and its input signals coming from several more connectors. This resulted in the uneconomical use of many separate connectors. Also, in order to maintain the integrity of the fault isolation in some systems of the prior art using this multi-connector scheme, a circuit card assembly could only contain one fault containment module.